<em># 导入包</em>
import 'package:flutter_web/<u>gestures</u>.dart'; 		<em>// flutter_web</em>
import 'package:flutter/<u>gestures</u>.dart'; 			<em>// flutter app</em>

<u>C</u>(
	<b>DragStartBehavior</b>: 	<q>DragStartBehavior</q>. 	<i>start</i> 		<em>// </em>
											<i>down</i> 		<em>// </em>
)